System for controlling light patterns with a high contrast

ABSTRACT

A system to produce a visual presentation on a screen such as alpha-numeric indications characterized by a switching element which is a matrix of individually controlled liquid crystals, a converging lens system, a plane filter located at the focal point of the lens system, and a screen. The matrix of liquid crystals includes means to render discrete liquid crystals in a condition to diffuse and scatter the light beams being projected therethrough. By selectively rendering specific liquid crystals of the matrix in the scattering condition, a source of parallel light can be converted to a specific pattern which is passed through a convergent lens system, through the plane filter such as an iris or aperture in a partition extending perpendicular to the parallel light beams and projected on a screen to produce the desired indication. Preferably, the source of light is obtained from a laser.

xi i 397509136 tteess July 351, W71} [54] SYSTEM EFQR C(DN'EEQQDLLHNGLHQQLHIT 3,620,598 11/1971 Brandt 350/162 SF lPlt'iTlEiPtNS Wllililil AQQN'KEUWT Prr'mar Examiner-1ohn W. Caldwell {75] inventor: BMW RWSSPlanegg Germany rissista it Examiner-lviarshall M. Curtis [73] Assignee:Siemens Ahtientgeseilimimilfil, Berlin Attorneyll, S Mcflmi, GrowSimpson and Munich, Germany 122 Filed: set. 22, isn't 157] WHEN"? Asystem to produce a visual presentation on a screen i211 PP N05 7327such as alpha-numeric indications characterized by a switching elementwhich is a matrix ofindividually con- [3()] FDR-again Appglicmian ga Damtrolled liquid crystals, a converging lens system, a plane A r 13 1970German P 20 17 615 2 filter iocated at the focal point of the lenssystem, and p y a screen. The matrix of liquid crystals includes means rto render discrete iiquid crystals in a condition to difg 346M324340/336 55 2 2; fuse and scatter the light beams being projected there{58] Field h I I h 1 l R through. By selectively rendering specificliquid crys- 162 SF 1 tals of the matrix in the scattering condition, asource 0 ara e 1 teen e converte to a s eci lC attern fp llll'gh b d p't' p [56} Reiemmes (0mg which is passed through a convergent lenssystem, T through the plane filter such as an iris or aperture in aUNHTED STATES PATEN'lS partition extending perpendicular to the parallellight 3,085,469 4/1963 Carlson 350/162 SF beams and projected on a creento produce the deg lg l et sired indication. Preferably, the source oflight is ob- 1 y a Win CI 21 3,536,376 10/1970 Henning 350/162 sr tamedfrom a 3,499,112 3/1970 Heilmeier et a1. 340/324 R 5 Cinirns, 3 DrawingFigures 0R mam/324R PATENTEDJUUI I975 3.750136 INVENTOR fl/e/er BoessATTYS.

ll SYSTEM FOR CONTROLLHNG LIGHT PATTERNS WHTH A HIGH CONTRAST BACKGROUNDOF THE INVENTION 1. Field of the Invention The present invention isdirected to a system for creating alpha-numeric indicators byselectively blocking portions of a source of parallel light rays.

2. Prior Art Some organic compounds while in a fluid state displaycrystal properties such as double refraction or birefringence and willtransmit a light beam without scattering. However, these compounds alsohave a condition in which they will diffuse and scatter a light beam andthus appear opaque or appear to block the passage of a light sourcetherethrough. The compounds can be switched from one state to the otherby the application of a magnetic or electrical force. A rather detaileddiscussion of liquid or fluid crystals is contained in an article byGeorge H. l-ieilmeier, Lewis A. Zanoni and Lucian A. Barton, DynamicScattering: A New Electrooptic Effect in Certain Classes Nematic LiquidCrystals. Proceedings of the IEEE Published by The Institute ofElectrical and Electronics Engineers, Inc., Volume 56, No.7, July 1968,Pages 1162-1171.

In the above-mentioned article, it is suggested that a matrix of liquidcrystals could be utilized in applications to form alphanumericindications. It has been suggested that by projecting parallel lightbeams onto a matrix of liquid crystals with each of the crystals beingindividually controlled, the matrix could be controlled to pass thelight beams through particular areas therein while scattering the lightbeams in the remaining areas so that the light when projected on ascreen would produce the desired indication. However, since the liquidcrystal always passes any light projected thereon, and depending on itscondition either transmits the light in an uninterrupted manner ordiffuses or scatters the light to give the appearance of blocking theflow of light therethrough, the diffused or scattered light causes abackground illumination of the screen which reduces the contrast betweenthe desired indication on the screen which are the light spots orportions and the dark areas which are created by the scattering of thelight beams to cause loss of contrast of the indication. In other words,the dark area on the screen created by scattering the light beamsdirected thereon receives enough illumination to reduce the contrastbetween them and the areas receiving the uninterrupted light beams toreduce the contrast of the indication and the background lighting of thescreen.

SUMMARY OF THE INVENTION The present invention is directed to a systemfor producing selected patterns in a light beam such as providing meansto selectively transmit the light beams in a desired area taken alongthe plane perpendicular to the path of the light beams, filter means toblock passage of undesired light rays, and a screen on which the lightbeams are projected. In the preferred embodiment the means fortransmitting the light beams in a particular area is a switching elementhaving a matrix of individually controlled liquid crystals disposedperpendicular to the path of the light beams. The filter means includesa means such as a lens system for converging the light beams that areselectively transmitted by the switching element at a focal point and aplane filter located at the focal point for blocking the light rays notconverged to the focal point. The plane filter is preferably a partitionhaving an aperture or means forming an iris.

Accordingly, an object of the present invention is to provide a systemfor selectively transmitting a light beam to form light patterns such asalphanumeric indications on a screen.

Another object of the present invention is to provide a system forforming light patterns such as alphanumeric indications on a screen withan increased contrast between the indication and the backgroundillumination to enable better recognition of the particular patternprojected thereon.

Other objects, features and advantages of the present invention will bereadily apparent from the following description ofa preferred embodimentthereof taken in conjunction with the accompanying drawings althoughvariations and modifications may be effected without departing from thespirit and scope of the novel concept of the disclosure.

BRIEF DESCRIPTlON OF THE DRAWlNGS FIG. 1 is a plan view of a screen ofan alphanumeric system incorporating the present invention;

FIG. 2 is a diagrammatic presentation of the present invention; and

FIG. 3 is a plan view of a matrix of liquid crystals used as a switchingelement in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principles of the presentinvention are best illustrated in FIG. 2 in which a beam 1 of parallellight rays is applied as an incident beam on a switching element 2 whichis capable of selectively passing the rays of the beam of parallel rays1 as parallel rays or scattering them into non-parallel rays. The lightpassing through the switching element 2 is thus directed to a filtermeans including a means for converging the parallel rays illustrated asa lens 3 and a plane filter 4. The lens 3 is positioned to receive thelight rays passing through the switching element 2 and converges theparallel rays to a focal point 7 where the plane filter 4 which isillustrated as a partition having an aperture or means forming an iris 8therein is located. Once the rays of light focused by the lens 3 passthrough the iris 8 of the filter 41, a second lens system or lens meanssuch as a lens 5 is used to convert the diverging rays into parallelrays which are then projected on a screen 6.

The beam of parallel light rays are preferably provided from a laserbeam because they havea particularly good parallelity, aremonochromatic, and have plane wave fronts which are practically notinfluenced by defraction. Thus, by use of a laser beam, the converginglens means such as the lens 3 can focus the beams at the focal point 7with a good concentration and minimal amount of overlap which sharplylimits any scattering of the light beams as they pass through the iris 8of the partition forming the filter 4.

As illustrated in FIG. 3, a switching element 2 is a matrix of aplurality of liquid crystals 10 in a raster or screen patternarrangement which crystals have a geometric shape such as theillustrated square configuration in a plane extending perpendicular tothe parallel light rays l. The liquid crystals can have any geometricconfiguration and each crystal has appropriate electrodes which enablethe changing of the crystal from a light-transmitting condition to alight-scattering condition. An example of an organic compound which canbe utilized for the liquid crystals is Anisylidene-paminophenylacetate.Another example of a compound which will act as a fluid crystal is4-rnethoxy-4-(nbutyl) benzylidene aniline. Various structuralarrangements for operative liquid crystals are discussed in theabove-mentioned article by George H. l leirnmer, Lewis A. Zanoni andLucien A. Barton, Dynamic Scattering: A New Electrooptic Effect inCertain Classes of Neumatic Liquid Crystals," Proceedings of the IEEE,Published by the institute Electrical and Electronic Engineers, lnc.,Volume 56, No. 7, fuly i968 and the disclosure of this article isthereby incorporated by reference thereto.

As illustrated in FIG. 3, a selected number of the liquid crystals whichare identified by the numeral ill are in a condition to transmit thelight without any scattering. The remaining crystals 12 of the matrixforming the switching element 2 are in a condition to scatter the light.Thus, parallel light beams are scattered with the unaffected parallellight beams having a pattern in a plane perpendicular to the parallelbeams which assume the shape of parallel light-transmitting crystal ill.and as illustrated a T-shape. As a result, after passing through theconverging lens 3, the plane filter 4", and the second lens system suchas the lens 5, a pattern 13 of light and dark areas with the light areashaving a T- shape is projected on the screen 6 to provide the particularindication. By selectively switching each of the liquid crystals betweenthe condition for transmitting light in an unaffected condition and acondition for scattering light, any light pattern such as any letter ofthe alphabet or any numeral can be produced.

it should be pointed out, however, that each of the crystals 10 istransmitting light regardless of its particular condition, the onlydifference is whether the light is still in a substantially parallelbeam or whether it is being diffused or scattered into divergent patterncharacteristics of the scattered condition. Thus, to project the lightbeams passing through the switching element 2 directly on a screen suchas 6, the light passing through the cells 10 that are in a scatteringcondition create a background illumination on the screen 6 which reducesthe contrast between the light area caused by the parallel light beamshitting the screen and the darlt area of the screen and causesdifficulties for an operator or person to recognize the symbol or figurebeing produced on the screen 6.

By providing the filter means comprising the lens 3 for converging theparallel light beams into a focal point 7 and a plane filter 4 locatedat the focal point 7' for the lens, the contrast of the symbol projectedon the screen 6 over the background lighting of the dark area on thescreen is greatly increased. This is understood by the fact that thelens 3 which can be either a single lens or a plurality of lens of themeans for converging or focusing the parallel beams focuses a majorityof the parallcl beams at the focal point 7. The filter 4 is illustratedas a partition having an aperture or iris 8 so that the light focused tothe focal point 7 of the lens 3 passes through the aperture and then isconverted back to parallel beams by the second lens system such as lensto be projected on the screen 6. The light, which was scattered by thecells 12 in the scattering condition of the switching element 2, due tothe different angles of incidence on the lens 3 will be focused by thelens 3 at a plurality of focal points which are randomly offset from thefocal point 7. The filter 4 with the aperture til at the focal point 7of the lens 3 will only allow passage of the light beams which areconverged to focal point 7 and blocks the light of the scatter lightbeams. Thus the filter 4 will reduce the amount of background light fromthe scattered light waves passing through the crystals which are in ascattering condition and decrease the illumination of the areas whichshould be dark for a particular indication.

in order to be able to recognize the information projected on the screen6, which information is fed into the switching element 2 by its controlmeans, the resolving powers of the system are of basic importance. Thespectoral function, the Fourier transforms, can be derived from acertain distribution of bright and dark places on the switching element2, for instance the pattern of parallel light-transmitting crystals ascompared to the pattern of defracting crystals. The spacial pictoralcomponents of the information-carrying light beam correspond to thediffraction at the bright-dark interfaces in the switching element.Since these spectoral components are important for recognizability ofthe information respectively contained in the switching element andsuperimposed into the light beam, it is necessary to increase the holediameter of the aperture or iris 8. Thus in selecting the size of theiris 8 for the partition 4, consideration must be given for blocking outthe transmission of the scattered light waves, yet the size of the irisshould not be so small as to cause defraction of the light beams passingtherethrough, or of a size to destroy by diffraction a part of theinformation-carrying light beams being focused and passed therethrough.Thus the size of this iris is selected to block out a majority of thescattered light waves without causing distortion of the focused parallellight beams carrying the particular information such as the alphanumericindication.

in selecting the size of the aperture when no information is to beindicated on the screen 6, the aperture is preferably several wavelengths of the light beam 1', however, to provide an informationindication, the aperture opening must be essentially larger. It shouldalso be pointed out that no lens is exactly perfect in focusing allparallel rays at a single focal point; therefore, the size of theaperture or iris must also include some tolerance for the tolerance inthe focal point of the lens systern.

The aperture 8 may be an adjustable iris which is adjusted in order tobe able to provide the best reproduction and resolution of the symbolsfor the particular system arrangement. The opening of the iris, however,is independent of the size of the picture and it has been suggested thatthe iris be a transparent member which has a gradual transition from acenter which is fully permeable to light to impermeable outer area. Theuse of an adjustable iris or an iris that has a gradual transition fromfully permeable to impermeable condition for light enables properselection of the size of the iris to obtain the correct resolutionnecessary for proper reading of the figure or symbol. it should bepointed out, that, if the beams passing through the liquid crystals aretoo sharply focused, they may appear as dots or other geometricconfigurations on the screen which may cause difficulties in determiningthe nature of the symbol being projected.

While this discussion has been directed to a matrix of liquid crystalswhich are used as a switching element, it is possible to use otherswitching elements which will allow the transmission of parallel lightbeams in a particular pattern when viewed along a plane extendingperpendicular to the light beams.

Although various minor modifications might be suggested by those versedin the art, it should be understood that 1 wish to embody within thescope of the patent warranted hereon all such modifications thatreasonably and properly come within the scope of my contribution to theart.

I claim as my invention:

1. An arrangement for producing a pattern in a beam of directional lightrays projecting on a screen to create an image thereon, comprising ascreen, a light beam switching element with selectively controllableareas along a plane extending transverse to the axis of said beam forscattering portions of the directional rays of the beam to create apattern of scatter rays and unscatter rays in the beam, and a filtermeans disposed between said switch element and said screen for blockingthe scatter rays as it passes the unscatter rays to improve the contrastbetween the image and background illumination on said screen, saidfilter means consisting of means for converging the unscatterdirectional rays to a focal point and a plane filter comprising apartition with means forming an iris therein, said plane filter beingdisposed with the iris means at said focal point and the partitionextending transversely to the axis of the beam whereby the filter meansreduces background illumination of the screen which is caused by thescattered rays being projected on the screen.

2. An arrangement according to claim 1, characterized in that theswitching element is a matrix of individual liquid crystals each ofwhich is selectively controlled between a light-transmitting conditionand a light-scattering condition.

3. An arrangement according to claim ll wherein the means forming aniris is an aperture in the partition.

3. An arrangement according to claim 1 wherein the means forming an irisis a transparent member with a center fully permeable to lightsurrounded with an outer area impermeable to light.

5. An arrangement according to claim 4, wherein the means forming aniris has an immediate area between the center and outer area to providea gradual transition from said permeable center to the impermeable outerarea.

1. An arrangement for producing a pattern in a beam of directional lightrays projecting on a screen to create an image thereon, comprising ascreen, a light beam switching element with selectively controllableareas along a plane extending transverse to the axis of said beam forscattering portions of the directional rays of the beam to create apattern of scatter rays and unscatter rays in the beam, and a filtermeans disposed between said switch element and said screen for blockingthe scatter rays as it passes the unscatter rays to improve the contrastbetween the image and background illumination on said screen, saidfilter means consisting of means for converging the unscatterdirectional rays to a focal point and a plane filter comprising apartition with means forming an iris therein, said plane filter beingdisposed with the iris means at said focal point and the partitionextending transversely to the axis of the beam whereby the filter meansreduces background illumination of the screen which is caused by thescattered rays being projected on the screen.
 2. An arrangementaccording to claim 1, characterized in that the switching element is amatrix of individual liquid crystals each of which is selectivelycontrolled between a light-transmitting condition and a light-scatteringcondition.
 3. An arrangement according to claim 1 wherein the meansforming an iris is an aperture in the partition.
 4. An arrangementaccording to claim 1 wherein the means forming an iris is a transparentmember with a center fully permeable to light surrounded with an outerarea impermeable to light.
 5. An arrangement according to claim 4,wherein the means forming an iris has an immediate area between thecenter and outer area to provide a gradual transition from saidpermeable center to the impermeable outer area.